Embodiments of the invention pertain to systems and methods for testing chlorine content of a water source. More specifically, embodiments relate to chlorine testing systems and methods that utilize chemically treated test strips to determine an amount of free chlorine and total chlorine that are present in a water source.
Chlorine has been used to disinfect water in industrial applications since the early 1800's, and is widely used today for example to disinfect water in swimming pools and spas. Hydrochloric acid, hypochlorous acid and the hypochlorite ion are formed when chlorine is added to water. Chlorine existing in water in these acid and ion forms is known as “free chlorine” and is a bactericide available to kill bacteria, algae, and disease carrying or causing organisms. “Combined chlorine” is formed when free chlorine has killed the contaminants, which contain ammonia, in the water source. These chloramines may include monochloramine, dichloramine and nitrogen trichloride. Once free chlorine undergoes a reaction to form these combined chlorines, it is no longer effective as a sanitizer. “Total chlorine” is the sum of free chlorine plus combined chlorine. Thus, total chlorine may include 100% free chlorine, 100% combined chlorine or some ratio there between.
There are various systems and/or methods for testing the amount of free chlorine that is available in a water source. One such test method is OTO (ortho-toluidine), which is a liquid test method. In the presence of chlorine the OTO will turn a water sample yellow and the sample becomes a darker yellow as the amount of chlorine increases. Another test method is known as DPD, which is shorthand for N,N-diethyl-para-phenylenediamine. It is available as a liquid, powder or tablet type of test. There are several types of DPD test methods, but the most widely used is colorimetric DPD, whereby the N,N-diethyl-para-phenylenediamine is oxidized by chlorine creating a magenta color. The intensity of the color is directly proportional to concentration of chlorine in the water.
Still another method of testing water that is different from the liquid, powder, or tablets mentioned above, includes test strips. Test strips are similar to the DPD test in that they are designed, and able to test for free chlorine and chloramines. The test strips typically include two test areas on a substrate that are chemically treated with a chlorine indicator such as syringaldazine and/or tetramethylbenzidine (also known as TMB), which are color responsive to chlorine and chloramines.
Test strips are typically sold in a container that has a label on the container, or an insert within the container, that includes a color scale to determine or estimate a concentration of free chlorine in a water source relative to a concentration of total chlorine, total chlorine being the sum of both free and combined chlorine. These test strips are used by consumers and professionals to determine if it is necessary to “shock” treat a water source such as a swimming pool or spa. Shocking, also known as super chlorinating, is a regular maintenance step for a pool. This treatment keeps pool water safe and clean by adding three to five times the normal amount of chlorine, or other chemical sanitizer, to the pool water to drastically raise the chlorine level for a short time. This helps to remove ineffective chlorine amounts, kills bacteria and anything organic in the pool, and boosts the availability of effective or free chlorine.
A typical color scale for test strips is shown in FIG. 1 and includes two rows 10, 12 of colored blocks 14, 16, respectively. The blocks 14 of row 10 represent different concentrations of total chlorine as indicated by the color of a respective block. The blocks 16 of row 12 represent different concentrations of free chlorine as indicated by the color of a respective block. The colors of the blocks 14, 16 in each row range from white or off-white to a purple or a deep purple color. A number is below each block and each number indicates a concentration level of total chlorine or free chlorine in parts per million of a water sample tested.
The test strip is dipped into a water source and agitated within the water for a time period, e.g., 30 seconds. Once removed, the user of the test strip observes the color change of the test areas to determine the amount of total chlorine and the amount of free chlorine detected. The user then calculates the amount of combined chlorine present in the water source, by subtracting the concentration of free chlorine from the concentration of total. If the amount of combined chlorine exceeds the amount of free chlorine available in the water source, the user should shock treat the water source.
A drawback with this test strip test method is that consumers who maintain their own pool and/or spa may find this quantitative method confusing in terms of calculating the amount of combined chlorine in the pool relative to the amount of free chlorine available. Moreover, a consumer user may not understand or appreciate the differences between total, free and combined chlorine.